With the development of display technology, the flat panel device, such as Liquid Crystal Display (LCD) possesses advantages of high image quality, power saving, thin body and wide application scope. Thus, it has been widely applied in various consumer electrical products, such as mobile phone, television, personal digital assistant, digital camera, notebook, laptop, and becomes the major display device.
Generally, the liquid crystal panel comprises a color filter substrate, an array substrate, liquid crystal sandwiched between the color filter substrate and the array substrate and sealant. Metal lines are formed on the array substrate. The resistance and the RC delay due to the resistance of the metal lines have great influence on the performance of the liquid crystal display panel, and particularly to be more obvious to the large scale and high resolution liquid crystal panel. The array substrate of the present liquid crystal panel commonly utilizes Al-interconnection. The Al-interconnection has higher electrical resistivity and the RC delay coming along with is also larger, which are difficult to be applied for the large scale and high resolution liquid crystal display panel.
Compared with the Al-interconnection, the Cu-interconnection possesses lower electrical resistivity and the RC delay coming along with is smaller, which can satisfy the demands of constant size growing up and high resolution of the liquid crystal display panel. However, in the present Cu-interconnection process, the oxydol series (H2O2) is commonly utilized as the etching liquid. The issue remains as the etching liquid is in use: With the number increase of the etched substrates, the copper ion concentration of the etching liquid keeps going up. The H2O2 will have chemical change of acceleration decomposition under the function of the Copper ion, the reaction process is:
            H      2        ⁢          O      2        ⁢      →                              ⁢      Cuion      ⁢                            ⁢            H      2        +                  O        2            .      Furthermore, with the progress of the Cu-interconnection etching process, the copper ion concentration of the etching liquid keeps increasing. The decomposition rate of the H2O2 gets faster and faster. When the copper ion concentration exceeds 6000 ppm, the decomposition rate of the H2O2 will rapidly increase and generates a mass of gas which can cause the explosion of the apparatus. Therefore, as the copper ion concentration exceeds 6000 ppm, the new etching liquid has to be replaced, which greatly restricts the usage lifetime of the etching liquid and increases the production cost. Besides, with the copper ion concentration increase of the etching liquid, the etching rate of the etching liquid will also change. Thus, the stability and the yield of the product are influenced.